The compelling argument is that it should be quite obvious that companies do not speak for all of their employees, cause most of them are - to what degree can be argued until the end of time - basically coerced to express the "opinion" of the company. At most it's the opinion of the owners, artificially amplified.
And to the question why the owners should not be able to express themselves: They can express themselves individually all they want, but if they want to use a company to do it they should also be personally responsible for everything the company does. And since one of the primary reasons to have a company is to isolate the owners from being sued personally ... there's a bit of a problem here.
But that’s not the claim. A “company” doesn’t speak, individuals do. Just because the individuals do as a result of compensation, doesn’t mean they lose their right to free expression.
You’re focusing on the “group” aspect of this, but that’s irrelevant to the argument. A PR spokesperson has individual rights, even if they choose to use that voice to advance a company’s goals.
Yes, and the reasoning holds; an individual decides to do that. There’s a name on that check, a specific person who authorizes the transfer of funds. How could you ethically stop a person from authorizing that check?
Disregarding the fact that I see many ways to ethically stop corruption, when an individual *acts* in the name of a corporation, the action is a result of the corporation's functioning, not of the individual's will (were it not so, the individual would have misappropriated the funds, to my understanding).